Injection drug use is driving HIV epidemics in low/middle-income countries in Eastern Europe, Central Asia and Southeast Asia. Combined prevention and care for (including needle/syringe programs (NSP), medication- assisted treatment, and antiretroviral treatment), has greatly reduced HIV incidence among persons who inject drugs (PWID) in many high-income areas, to where the HIV epidemics among PWID have ended. There is now the need for a convincing demonstration that an HIV epidemic can be ended in a low/middle income setting. The overarching purpose of the proposed research is to demonstrate that high coverage implementation of combined prevention and care using an innovative approach will end the HIV epidemic among PWID in Haiphong, Viet Nam. The innovative approach consists of i) implementing repeated large community-based respondent driven sampling (RDS) surveys to reach and test a large proportion of PWID for HIV, and ii) mobilizing peer support groups to educate about the benefits of early ART, link HIV-infected PWID into HIV care and achieve viral suppression. Peer groups will also support safer injection, safer sex, and accessing methadone treatment for both HIV positive and negative persons. The research has five specific aims: 1. Demonstrate that the innovative approach can reduce PWID population viral load (the percentage of PWID with detectable HIV viral load) by at least half. 2. Assess progress towards ending the epidemic, using direct measurement of HIV incidence among PWID. The goal is to achieve an incidence of 0.5/100 PY or less (our operational definition of ending the epidemic'). 3. Utilize mathematical modeling to assess the contributions of different components of combined prevention and care to ending the epidemic among PWID in Haiphong. A model previously used in several other countries will be adapted to the Haiphong setting. 4. Assess the cost-effectiveness and cost savings of the proposed intervention activities to end the HIV epidemic among PWID in Haiphong. 5. Develop a large, high retention cohort of HIV+ and HIV- PWID for future collaborative research studies. Questionnaire data and biological samples from participants in the proposed study will be stored. We expect to have approximately 1500 active participants in the cohort at the end of the proposed research period. The feasibility of this ambitious proposal is ensured by i) the 2-year DRIVE-IN feasibility study we have already conducted in Haiphong, which assessed the situation and successfully piloted the intervention, ii) The existing good facilities for HIV care and MAT, iii) the strong local commitment of political and health authorities, pre-existing peer-support groups and NGOs, and iv) the DRIVE research consortium of Vietnamese, French and US researchers, a highly qualified team with a proven record of productive collaboration.